The present invention relates to a structural body and to a hollow extruded frame member used to form the structural body by friction stir welding. The invention relates more particularly to a novel joint shape of a structural body formed by joining hollow extruded frame members using friction stir welding.
The present invention relates to a structural body and hollow extruded frame members used in forming the structural body by friction stir welding, and the invention relates particularly to structural members suited to use, for example, as an aluminum alloy member of the type used in a railway vehicle and in building construction.
As described in Japanese application patent laid open publication No. Hei. 9-309164 (EP 0797043 A2), a friction stir welding method is a method in which, by rotating a round rod (referred to hereinafter as a rotary body) which is inserted into a joint between hollow extruded frame members to be joined and by moving the rotary body along a line of the joint between the frame members to be joined, the joint of the frame members is exothermally heated and softened and the joint is elastically fluidized to form a solid weld.
The rotary body for carrying out the friction stir welding comprises a small diameter portion which is inserted in the joint and a large diameter portion which is positioned outside the joint. The small diameter portion and the large diameter portion of the rotary body have the same axis. A boundary face portion between the small diameter portion and the large diameter portion of the rotary body is inserted a little into the joint. The welding according to the friction stir welding method may be applied to an abutting portion of two frame members or to an overlapping portion of the frame members.
As disclosed in the above-state publication, a protruding portion of a frame member is provided at the portion of the frame member to be subjected to welding. This protruding portion of the frame member comes into contact with the rotary body, so that the protruding portion of the frame member is welded using the friction stir welding method. As further disclosed in the publication, a protrusion chip is provided at the portion of the frame member to be subjected to welding. This protrusion chip protrudes from a rib of an end portion of one of the hollow extruded frame members to be subjected to welding toward the other hollow extruded frame member to which it is to be joined. On this protrusion chip a face plate of the other hollow extruded frame member is overlapped.
Since friction stir welding is carried out by inserting a rotary body serving as a joining tool into a joint between the hollow frame members to be welded causing metal to be fluidized, a large force is exerted on the frame members during welding. Namely, a large force is required for inserting the rotary body into the joint between the frame members to be welded, and so the frame members must be constructed to endure this large force. As a result, when the hollow extruded frame members are joined, as described in the above-stated publication, metal easily flows to a rear side of the joint. Therefore, it is necessary to make the protruding portion of the hollow extruded frame members rather large for supplementing the amount of metal which flows in the joint. Further, void holes occur easily in a joining bead of the frame members.
As one means for preventing the above-stated various defects, the thickness of the frame member to be subjected to welding is made large at the joint portion, thereby the flow-out of metal from the frame members can be prevented. For example, by giving a large circular arc shape to the corner between the face plate and the rib at the joining portion of the frame member, the thickness of an outer portion of the frame member to be subjected to welding can be increased. Further, for example, by making the diameter of the circular arc shape of the corner between the protrusion chip and the rib of the frame member large, the thickness of the outer portion of the frame member to be subjected to welding can be increased.
The above stated circular arc shape of the frame member to be subjected to welding is recessed toward a side of the fact plate of the frame member. Accordingly, the cross sectional area of the frame member to be subjected to welding becomes large, with the result that the weight of the frame member increases.